Positive electrode current collector for lead accumulator

ABSTRACT

In a positive electrode current collector for a lead-acid battery including a coating of tin dioxide formed on the surface of a current collector substrate of titanium or a titanium alloy, the half width of a peak with the maximum intensity among peaks of tin dioxide in the x-ray diffraction pattern of the positive electrode current collector for a lead-acid battery is 1° or lower.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a positive electrode current collectorfor a lead-acid battery having a coating on the surface.

2. Description of the Related Art

A lead-acid battery has a low energy density as compared with anickel-metal hydride battery and a lithium ion battery. One of thecauses is that lead or a lead alloy to be used as a positive electrodecurrent collector is thick and heavy. Therefore, use of titanium or atitanium alloy (hereinafter, referred to as titanium or the like) forthe positive electrode current collector and formation of a conductiveoxide layer of tin dioxide or the like as a coating on the surface oftitanium or the like have been proposed (reference to Japanese PatentApplication Laid-Open (JP-A) No. 55-64377 and Japanese Patent No.3482605). It is because use of titanium or the like makes a positiveelectrode current collector lightweight because of the lower specificgravity of titanium or the like than that of lead.

However, in the case where a positive electrode current collector madeof solely titanium or the like is used for a lead-acid battery, althoughhard, titanium or the like is slightly dissolved in diluted sulfuricacid, which is an electrolytic solution, and accordingly there occurs aproblem. Therefore, a tin dioxide which is insoluble in diluted sulfuricacid, which is an electrolytic solution, is formed as a coating on thesurface of titanium or the like.

Moreover, in the case of forming tin dioxide on the surface of titaniumor the like, there are advantageous points: (i) tin dioxide shows highelectrochemical stability when it is positive electrode potential in anelectrolytic solution; (ii) voltage decrease by existence of the coatingof tin dioxide with low conductivity can be suppressed by titanium orthe like with high conductivity; and (iii) since the melting point oftitanium or the like is high, it can stand firing around 500° C. in astep of forming a tin dioxide coating.

As a method for forming the tin dioxide coating on the surface of acurrent collector substrate are generally employed a dip coating methodand a spin coating method. Specifically, the coating of tin dioxide isformed by applying a raw material solution containing tin on titanium orthe like and thereafter heating them. Further, a technique of forming atin dioxide coating on the surface of a glass substrate by a spraymethod is also proposed (e.g., Japanese Patent No. 3271906, or J. J.Rowlette, American Chemical Society, 1052 (1986))

In Japanese Patent No. 3271906, in a first step, a first raw materialsolution obtained by dissolving an organic compound such as dibutyltindiacetate in an organic solvent is atomized in a spray form on thesurface of a heated glass substrate. At that time, in order to avoid afactor of crystallinity decrease, an element such as antimony andfluorine having outermost electrons in a number higher by one than thatof tin or oxygen is not added to the first raw material solution. Thesprayed first raw material solution is thermally decomposed on thesurface of the heated glass substrate to form an undercoating layerselectively oriented to a specified crystal plane. Next, a second rawsolution obtained by adding an element having outermost electrons in anumber higher by one than that of tin or oxygen to the first rawsolution is atomized in a spray form on the surface of the undercoatinglayer.

SUMMARY OF THE INVENTION

However, in the case where a lead-acid battery is produced using acurrent collector substrate of titanium or the like having a coating oftin dioxide on the surface, there is a problem that the life performanceof the lead-acid battery is inferior. The inventors of the presentinvention have made investigations on its cause and accordingly havemade it clear that the crystallinity of tin dioxide formed as a coatingaffects the life performance. Conventionally, no attention has been paidto the crystallinity of tin dioxide in form of the coating.

According to the dip coating method and spin coating method described inthe paragraphs of Related Art described above, in the case of formingtin dioxide on a current collector substrate of titanium or the like,the applied raw material solution is thermally decomposed from a surfaceside far from the current collector substrate. Therefore, crystal coresare produced in crystal planes having various directions on the surfaceside of the raw material solution and along with the proceeding of thethermal decomposition, crystals are respectively grown from the crystalcores. If the crystals of various crystal planes are grown, points wherethe crystals of different crystal planes are adjacent to one another areincreased to increase crystal strains. As a result, the crystallinitydecreases.

Further, in the case where the crystallinity decreases, points where thedistance between a tin atom and an oxygen atom is not as in a standardcrystal state are increased to lower the chemical stability.Accordingly, the life performance of a lead-acid battery using thecurrent collector substrate deteriorates.

Under the above-mentioned state of the problems, the present inventionaims to solve the problems according to the following means.

A positive electrode current collector for a lead-acid battery of thepresent invention is a positive electrode current collector for alead-acid battery including a coating of tin dioxide formed on thesurface of a current collector substrate of titanium or a titanium alloyand is characterized in that the half width of a peak with the maximumintensity among peaks of tin dioxide in the x-ray diffraction pattern ofthe positive electrode current collector for a lead-acid battery is 1°or lower.

In the case where a lead-acid battery is produced using such a positiveelectrode current collector, the life performance of the lead-acidbattery becomes excellent. The results of specific experiments will bedescribed later.

As titanium is used titanium (JIS 1 type) or titanium (JIS 2 type). As atitanium alloy are used Ti-5Al-2.5V, Ti-3Al-2.5V, and Ti-6Al-4V.

In the x-ray diffractometry of the present application, while x-ray(CuKα ray) is radiated to a specimen, scanning is carried out at anincident angle θ in a prescribed range and during that time, theintensity of diffracted x-ray is counted. If a diffraction angle 2θ isplotted in an abscissa axis and diffraction intensity is plotted in anordinate axis, the x-ray diffraction pattern is obtained. According tothe x-ray diffraction pattern, based on the crystal structure of tindioxide coating which is a specimen and the wavelength of radiatedx-ray, the types of crystal planes corresponding to the diffractionangles 2θ at which the peaks of the x-ray diffraction intensity appearcan be specified. In this application, 2θ is set in a range of 26.6° to108.4°.

The term “peaks” means hill-like parts in the x-ray diffraction pattern.The respective peaks correspond to crystal planes. The term “half width”means a diffraction angular width of the peak curve in the x-raydiffraction intensity at which the intensity (x-ray diffractionintensity at a summit in the peak curve) of the peak becomes ½. If thehalf width is narrow, the peak has a sharp hill-like shape and thecrystallinity of the crystal plane can be said to be high. On the otherhand, if the half width is broad, the peak has gentle hill-like shapewith a spread toward the bottom and the crystallinity of the crystalplane can be said to be low.

In order to produce such a positive electrode current collector for alead-acid battery, a production method described below may be employed.

The positive electrode current collector for a lead-acid battery of thepresent invention is a positive electrode current collector for alead-acid battery having a coating of tin dioxide formed on the surfaceof a current collector substrate of titanium or a titanium alloy and ischaracterized in that the above-mentioned crystals of tin dioxide areselectively oriented in 1 or more and 4 or less of the crystal planes.

In the case where a lead-acid battery is produced using such a positiveelectrode current collector, the life performance of the lead-acidbattery becomes excellent. Results of specific experiments will bedescribed later.

Herein, the phrase “selectively oriented in the crystal planes” meansthe case that the texture coefficient TC of the crystal planes is 1 ormore. For example, the texture coefficient TC of a (110) plane is 1 ormore, it can be expressed that the crystal is oriented in the (110)plane. A calculation method of the texture coefficient TC will bedescribed in a first embodiment.

The present invention is characterized in that the oriented crystalplanes as described above are a (110) plane, a (101) plane, a (200)plane, a (211) plane, a (220) plane, a (310) plane, a (112) plane, or a(301) plane.

In the case where titanium or the like has an oriented tin dioxidecoating on the above-mentioned crystal plane, the life performance ofthe lead-acid battery produced using the positive electrode currentcollector becomes excellent.

The present invention is characterized in that the coating containsantimony or fluorine in the positive electrode current collector for alead-acid battery.

Since the coating contains antimony or fluorine, the conductivity of thecoating is remarkably improved. In the case where the conductivity ofthe coating is high, since the inner resistance of the lead-acid batteryis lowered, the life performance of the lead-acid battery becomesfurther excellent and the effect of the present invention is moreapparently caused. In the case of comparison of antimony with fluorine,antimony is better.

A positive electrode current collector for a lead-acid battery having acoating on the surface of a current collector substrate of the presentinvention is produced by the following method. That is, the productionmethod involves a step of intermittently spraying a raw materialsolution obtained by dissolving a tin compound in a solvent to thesurface of a heated current collector substrate made of titanium or atitanium alloy.

Accordingly, a coating of tin dioxide with high crystallinity is formedon the surface of titanium or the like. As a result, in the case where alead-acid battery is produced using the positive electrode currentcollector produced by this production method, the life performance ofthe lead-acid battery becomes excellent.

In this production method, as the tin compound, organotin compounds suchas dibutyltin diacetate, tributoxytin, and the like and inorganic tincompounds such as tin tetrachloride may be employed. As a solvent, anorganic solvent such as ethanol, butanol, and the like may be employed.To add antimony to the raw material solution obtained by dissolving atin compound in a solvent, a method of mixing a chloride of antimony maybe employed.

In execution of the production method, it is required to heat thecurrent collector substrate in order to thermally decompose the tincompound in the raw material solution when the raw material solution issprayed to the current collector substrate. The temperature suitable forthe heating depends on the type of the tin compound. For example, in thecase of using a raw material solution obtained by mixing an antimonychloride solution (solvent:ethanol) with a dibutyl tin diacetatesolution (solvent:ethanol), the temperature is 400° C. or higher. It ispreferably 450° C. or higher and most preferably 500° C. or higher.

At the time of spraying the raw material solution to the surface of thecurrent collector substrate, spraying is repeated at intervals, so thatthe temperature is not decreased. That is, spraying is carried outintermittently.

The thickness of the coating of tin dioxide to be formed by one timespraying is required to be 5 nm or thinner. It is because a coating oftin dioxide with high crystallinity can be obtained by the productionmethod by which such a thin coating is layered. Further, it is becausecrystals of tin dioxide to be formed on the surface of titanium or thelike can be selectively oriented in one or more and 4 or less of thecrystal planes.

In order to form such a thin coating, it is preferable to adjust aspraying amount at one time is 0.4 cc or less. It is because, althoughit depends on other conditions for the production, 0.4 cc or less of thespraying amount is suitable for layering the coating of 5 nm or thinner.

The reason for the possibility of obtaining high crystallinity bylayering of the coating formed in such a thin thickness is not clearlyunderstood. However, it is probably attributed to that titanium oxideexisting on the surface of the current collector substrate and oxides oftitanium and tin formed in the initial stage of the coating formationbecome an undercoat layer and tin dioxide forming the coating isepitaxially grown. In this connection, tin dioxide cannot be selectivelyoriented in specified crystal planes by a conventional dip coatingmethod. Therefore, tin dioxide does not show high crystallinity.

In execution of the production method, it is preferable for the rawmaterial solution to contain antimony or fluorine. Existence of antimonyor fluorine in the coating improves the conductivity of the coating. Inthe case where the coating has high conductivity, since the innerresistance of the lead-acid battery is lowered, the life performance ofthe lead-acid battery becomes further excellent. In the case ofcomparison of antimony with fluorine, antimony is better.

The lead-acid battery of the present invention is characterized in thatthe battery is provided with the above-mentioned positive electrodecurrent collector. Accordingly, since the life performance of thepositive electrode current collector is heightened, the lead-acidbattery with high energy density and a long life can be provided in alow cost.

As described above, in the case where a lead-acid battery is producedusing a positive electrode current collector according to the presentinvention, the life performance of the lead-acid battery becomesexcellent.

The present application is based on Japanese Patent Application (JP-ANo. 2005-285131) filed on Sep. 29, 2005, the disclosure of which ishereby incorporated by reference in its entirety.

Finally, the relevancy of the present invention and the above-mentionedJapanese Patent No. 3271906 will be described. Japanese Patent No.3271906 discloses a production method of forming a tin dioxide coatingwith high crystallinity on the surface of a glass substrate. However,the production method described in Japanese Patent No. 3271906 does notrelate to a positive electrode current collector for a lead-acidbattery. The production method including a first stage and a secondstage described in Japanese Patent No. 3271906 is combined with titaniumor the like, which is a current collector substrate of a positiveelectrode current collector to be used in the present invention, sincethe conductivity of the undercoat layer formed in the first stagebecomes too low, only a positive electrode current collector whichcannot be practically usable as the positive electrode current collectoris obtained. The production cost is also increased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing an x-ray diffraction pattern of a tin dioxidecoating in a positive electrode current collector according to Exampleof the present invention;

FIG. 2 is a view showing the results of a life test according to Exampleof the present invention;

FIG. 3 is a vertical cross sectional view showing the structure of acell using the current collector substrate of titanium for a positiveelectrode plate according to Example of the present invention;

FIG. 4 is a vertical cross sectional view showing the structure of alead-acid battery having four combined cells shown in FIG. 3 accordingto Example of the present invention;

FIG. 5 is a view showing an x-ray diffraction pattern of a positiveelectrode current collector, in which the heating temperature of thecurrent collector substrate is changed, according to Example of thepresent invention;

FIG. 6 is a view showing a relation between the half width of a peakwith the maximum intensity among peaks of tin dioxide in the x-raydiffraction pattern of the positive electrode current collector and thelife performance; and

FIG. 7 is a view showing a relation between the number of crystal planeshaving oriented tin dioxide crystals and the life performance.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (1) First Embodiment(1.1) Production of Positive Electrode Current Collector

In Example 1, a mixed solution of a dibutyltin diacetate solution(solvent: ethanol) and an antimony chloride solution (solvent: ethanol)was used as a raw material solution. In this case, the amount ofdibutyltin diacetate was adjusted to be 2.5% by mass on the basis of tindioxide in the entire raw material solution. Further, the amount ofantimony chloride was adjusted to be 2.5% by mass on the basis ofantimony to tin dioxide.

The raw material solution was intermittently sprayed to the surface of aflat plate-like current collector substrate heated to 450° C. At thetime of spraying, the spraying intervals were controlled so as to keepthe temperature of the current collector substrate at 450° C.Accordingly, thermal decomposition is caused on the surface of thecurrent collector substrate to form a coating of tin dioxide. Theobtained substrate was set as a positive electrode current collector ofExample 1.

Next, to compare with Example 1, a positive electrode current collectorof a conventional example 1 was produced. The conventional example 1 wasproduced by a dip coating method using a raw material solution preparedby dissolving tin tetrachloride, antimony trichloride, and a smallamount of hydrochloric acid in propanol. That is, a flat plate-likecurrent collector substrate similar to that of Example 1 was immersed inthe raw material solution, pulled up at 30 cm/min, dried for 15 minutes,and thereafter kept still in an electric furnace heated to 500° C. for30 minutes to form a tin dioxide coating. The obtained substrate was setas a positive electrode current collector of the conventional example 1.

(1.2) Results of X-Ray Diffractometry

FIG. 1 shows the x-ray diffraction pattern of the positive electrodecurrent collector of Example 1 and the x-ray diffraction pattern of thepositive electrode current collector of the conventional example 1. TheXRD peak of Example 1 is sharp as compared with that of the conventionalexample 1.

Table 1 shows the half width of a peak with the maximum intensity inExample 1 and the conventional example 1. The crystal plane of the peakwith the maximum intensity is a (200) plane for Example 1 and a (110)plane for the conventional example 1.

TABLE 1 Crystal plane Half width Conventional example 1 (110) 2.21°Example 1 (200) 0.68°

As shown in Table 1, in the conventional example 1, the half width ofthe peak of the (110) plane in which the intensity was the maximum wasrather higher than lo. On the other hand, in Example 1, the half widthof the peak of the (200) plane in which the intensity was the maximumwas sufficiently lower than 10.

Accordingly, in the case of the tin dioxide coating of the conventionalexample 1, it is supposed that the crystallinity of the coating is lowand points where the distance between a tin atom and an oxygen atom isnot as in a standard crystal state are many. On the other hand, in thecase of the tin dioxide coating of Example 1, it is supposed that thecrystallinity of the coating is high and points where the distancebetween a tin atom and an oxygen atom is as in a standard crystal stateare many.

Next, the texture coefficient TC of each crystal plane in Example 1 andthe conventional example 1 was calculated. The results are shown inTable 2.

Herein, “texture coefficient TC” is an index for evaluating orientationof a crystal plane which can be calculated according to the followingexpression (1). In the expression (1), I(hkl) is an x-ray diffractionintensity in a (hkl) plane; I₀ (hkl) is a standard intensity of eachcrystal plane of a tin dioxide obtained according to JCPDS (No.41-1445). N denotes the number of diffraction lines. Herein, calculationwas carried out using diffraction line number N=31 (2θ=26.6° to 108.4°).Accordingly, if the texture coefficient TC is 1 or lower, no crystalorientation occurs in the crystal plane and if it is 31, the maximumvalue, the crystal is completely oriented in the crystal plane and itmeans that the orientation becomes higher as the texture coefficient TCis further higher than 1.

However, in the calculation method according to the following expression(1), even if a crystal with high orientation is not actually formed in acrystal plane with a small standard intensity, 1 or higher texturecoefficient TC is sometimes given by the calculation. Accordingly, thefollowing crystal planes were selected; a (110) plane, a (101) plane, a(200) plane, a (211) plane, a (220) plane, a (310) plane, a (112) plane,and a (301) plane; which are crystal planes having standard intensity of10 or higher in the case where the standard intensity of a (110) planehaving the highest standard intensity obtained from the JCPDS was set tobe 100 and the texture coefficient TC was calculated only for 8 kinds ofthem according to the expression (1) to employ the resulting values asthe orientation indications.

Expression 1

TABLE 2 (1) $\begin{matrix}{{TC} = \frac{\frac{I\left( {h{\mspace{11mu} \;}k\mspace{14mu} 1} \right)}{I_{0}\left( {h{\mspace{11mu} \;}k\mspace{14mu} 1} \right)}}{\frac{1}{N}{\sum\limits_{N}\; \frac{I\left( {h{\mspace{11mu} \;}k\mspace{14mu} 1} \right)}{I_{0}\left( {h{\mspace{11mu} \;}k\mspace{14mu} 1} \right)}}}} & \mspace{11mu}\end{matrix}$ Crystal plane of tin Texture coefficient TC dioxide (hkl)Conventional example 1 Example 1 (110) 0.53 0.32 (101) 0.33 0.52 (200)0.71 3.21 (211) 0.36 0.68 (220) 0.56 0.28 (310) 0.52 0.68 (112) 0.550.42 (301) 0.42 1.34

As shown in Table 2, the texture coefficient TC of each crystal planewas sufficiently lower than 1 in the case of the tin dioxide coating ofthe conventional example 1 and the crystal was not selectively orientedin any crystal plane and the crystallinity was thus inferior. On theother hand, since the texture coefficient TC of the (200) plane and the(301) plane was 1 or higher and crystal was selectively oriented inthese two types of crystal planes in the case of the tin dioxide coatingof Example 1.

(1.3) Life Test

FIG. 2 shows a life test using positive electrode current collectors ofExample 1 and the conventional example 1. The method of the life testwas as follows.

At first, according to a common production method of a lead-acidbattery, an active material paste was produced by kneading a leadpowder, water, and sulfuric acid. Thereafter, the active material pastewas packed in a frame with 10 mm in diameter×8 mm in thickness and driedto obtain active material pellet. The pellet was put in a dilutedsulfuric acid solution with a concentration of 20% and electric currentat 50 mA was applied to carry out formation and charging.

The active material pellet was formed in a flat plate-like shape and puton the positive electrode current collectors of Example 1 and theconventional examples 1 and 2 and while being press-bonded by pressurearound 100 kPa, these active material pellet and positive electrodecurrent collectors were immersed in a diluted sulfuric acid solutionwith a concentration of 40% to obtain positive electrode plates. A leadplate was used as a negative electrode plate.

Respective test cells were assembled using the above-mentioned positiveelectrode plates and negative electrode plate. Constant voltage of 2.3 Vwas applied to the respective test cells to carry out a constant voltageovercharging test at 650° C. in a vapor phase.

The test cells were periodically taken out of the test environments andleft at room temperature for 24 hours. Thereafter, discharge at 150 mAwas carried out to measure the positive electrode capacities. The momentthe measured positive electrode capacity became below 50% of the initialvalue was determined to be the time of termination. The days until thetime the life was terminated was defined as the life performance (days).

The results of the life test according to the above-mentioned method areshown in FIG. 2. FIG. 2 also shows the results of a test carried out forcomparison of a positive electrode current collector of a conventionalexample 2 obtained by electrodepositing a lead dioxide layer on thesurface of the tin dioxide coating formed in the conventional example 1.The tin dioxide layer was carried out by electrodeposition by applyingelectric current at current density of 5 to 10 mA/cm² and a temperatureof 40 to 50° C. in a 4 to 5 N sodium hydroxide solution in which leadhydroxide was saturated.

According to FIG. 2, the life performance of the positive electrodecurrent collector of the conventional electrode 1 was shorter than 100days. On the other hand, the life performance of the positive electrodecurrent collector of Example 1 exceeded 400 days. Even beyond 400 days,decrease of the positive electrode capacity was slight. The lifeperformance of the positive electrode current collector of theconventional example 2 slightly exceeded 200 days.

Herein, the life performance of the normal lead-acid battery measured inthe constant voltage overcharging test at 65° C. is around 120 days inthe case of a common product and it is around 240 days in the case of aproduct planed to have a long life. Accordingly, it can be said that thecycle life performance of the lead-acid battery using the positiveelectrode current collector of Example 1 is remarkably excellent ascompared with those of these common product and product planed to have along life.

(1.4) Production of Cell, Production of Lead-Acid Battery, and Life Testof Lead-Acid Battery

A cell 1 was produced using the positive electrode current collector ofExample 1. A cell 1 was produced using the positive electrode currentcollector of the conventional example 1

The structure of the cell 1 is shown in FIG. 3. A battery case 4 is aninsulating frame body for an air-tightly housing a positive electrodeactive material 5, a separator 6, and a negative electrode activematerial 7 and sandwiched between a positive electrode current collector2 and a negative electrode current collector 3. The battery case 4 isprovided with a gas discharge port 4 a communicated to the outside. Theaperture part of the gas discharge port 4 a is provided with a controlvalve 8. The positive electrode active material 5, the separator 6, andthe negative electrode active material 7 are arranged in the inside ofthe battery case 4. The positive electrode active material 5, theseparator 6, and the negative electrode active material 7 areimpregnated with an electrolyte solution containing diluted sulfuricacid as a main component.

The positive electrode current collector 2 was provided with thepositive electrode active material 5 to produce a positive electrodeplate. Herein, the positive electrode active material 5 was a plate-likeactive material containing mainly lead dioxide (PbO₂). The negativeelectrode current collector 3 was a copper plate (thickness: 0.1 mm)plated with lead (thickness: 20 to 30 μm). The negative electrodecurrent collector 3 was provided with the negative electrode activematerial 7 to produce a negative electrode plate. Herein, the negativeelectrode active material 7 was a plate-like active material of mainlysponge-like metal lead. The separator 6 was like a mat produced fromglass fibers. The positive electrode plate and the negative electrodeplate were layered with the separator interposed therebetween and housedin a container. The container was covered with a cover and theelectrolyte solution was injected to produce the cell 1 of a lead-acidbattery.

Next, a lead-acid battery of Example 1 was produced using four cells 1produced using the positive electrode current collector of Example 1.Further, a lead-acid battery of the conventional example 1 was producedusing four cells 1 produced using the positive electrode currentcollector of conventional example 1. The configuration example is shownin FIG. 4. The lead-acid batteries are lead-acid batteries for anuninterruptible power supply apparatus (hereinafter, referred tolead-acid battery for UPS using UPS as abbreviation of UninterruptiblePower Supply). The lead-acid battery produced using the positiveelectrode current collector of the present invention was remarkablyexcellent in the life performance and therefore was particularly usefulfor UPS.

The negative electrode current collector 3 of the cell 1 was set on thepositive electrode current collector 2 of another cell and in such amanner, four cells 1 were layered and connected in series. The pressingmembers 9 and 10 made of a conductive material such as a metal platewere set on the top and the bottom of the four cells 1. Thecircumferences of the cells were surrounded with an auxiliary framematerial 11 of an insulating material such as a resin or the like. Thepressing members 9 and 10 were fixed respectively in the top and bottomend faces of the auxiliary frame material 11 with a plurality of screws12 to firmly press, pinch, and fix the four cells 1. These pressingmembers 9 and 10 were directly press-bonded with the positive electrodecurrent collector 2 and the negative electrode current collector 3 andtherefore, they could be used as positive and negative electrodeterminals.

Herein, in the respective pinched and fixed cells 1, the separators 6were in compressed state. Due to the repulsive force, the positiveelectrode active material 5 was pushed to the positive electrode currentcollectors 2 at gauge pressure of around 250 kPa and the negativeelectrode active material 7 was pushed to the negative electrode currentcollectors 3. To obtain the pressing force by the separators 6, thematerial and the thickness for the separators 6 may be adjustedproperly. The pressing force can be changed properly in accordance withthe structure, the capacity, and the size of the cells 1. Generally, thecharge discharge performance can be stabilized by applying gaugepressure of around 100 to 400 kPa.

With respect to the lead-acid batteries of Example 1 and theconventional example 1 (nominal capacities are both 2.3 Ah), the energydensity per weight at the time of discharge at 0.5 A and the lifeperformance were compared. As a result, the energy density per weightwas 50 Wh/kg for both. The life performance was 15 months for Example 1and 7 months for the conventional example. The life performance ofExample 1 was remarkably excellent as compared with that of theconventional example 1.

(1.5) Production Cost

The cost to produce the positive electrode current collector of Example1 and the cost to produce the positive electrode current collector ofthe conventional example 2 are estimated. Both are compared. As aresult, the cost for producing the positive electrode current collectorof Example 1 is about one fifth of that of the conventional example 2.In the conventional example 2, since the lead dioxide layer waselectrodeposited further on the surface of the tin dioxide coatingformed by the dip coating method, the production efficiency was low. Theproduction method of the invention can be said to be excellent ascompared with the conventional production method.

(1.6) Others

In Example 1, dibutyltin diacetate was used for the raw materialsolution. However, even in the case where an organic tin compound suchas tributoxytin or an inorganic tin compound such as tin tetrachloridewas used, if the half width of a peak with the maximum intensity amongpeaks of tin dioxide in the x-ray diffraction pattern of the positiveelectrode current collector was 1° or lower, the life performance of thelead-acid battery using the positive electrode current collector wasexcellent.

Not limited to the case the selectively oriented crystal planes were(200) plane and (301) plane as Example 1, even in the case where theplanes were, for example, (110) plane, (101) plane, and (211) plane, thesame results were obtained. That is, it was confirmed that theorientation did not depend on the types of crystal planes.

Although at least one crystal plane is necessary for selectiveorientation, even in the case of 2 to 4 crystal planes, the same resultsof the test were obtained regardless of the combinations of thesecrystal planes. However, in the case of orientation in 5 or more crystalplanes, the points where the crystals of different crystal planes wereadjacent to each other were increased and therefore the crystallinitywas not sufficiently heightened and consequently, similar to the case ofthe conventional example 1, the life performance was not excellent.

In the lead-acid battery of the first embodiment, an example in whichfour cells 1 were combined was employed. However, the lead-acid batterymay be composed using only one or the lead-acid battery may be composedby combining an arbitrary number of 2 or more of cells 1. Further,although the screws 12 were employed for pressing the cells 1 by thepressing member 9 and 10 in the lead-acid battery, the fixation means isarbitrary. For example, it may be caulking.

(2) Second Embodiment (2.1) Production of Positive Electrode CurrentCollector

Positive electrode current collectors were produced while changing theheating temperature of the current collector substrates when the rawmaterial solution was intermittently sprayed to 300° C., 350° C., 380°C., 400° C., 420° C., 450° C., or 450° C. At the time of spraying, theheating temperature was prevented from lowering. The raw materialsolution to be used was the same raw material solution as in theabove-mentioned first embodiment.

The case where the heating temperature of the current collectorsubstrate was 300° C. was set to be Comparative Example 1; the case of350° C. was set to be Comparative Example 2; the case of 380° C. was setto be Comparative Example 3; the case of 400° C. was set to be Example2-1; the case of 420° C. was set to be Example 2-2; the case of 450° C.was set to be Example 2-3; and the case of 500° C. was set to be Example2-4.

(2.2) Results of X-Ray Diffractometry

In the x-ray diffraction patterns of the positive electrode currentcollectors of Comparative Examples 1, 2, and 3 and Examples 2-1, 2-2,2-3, and 2-4, the crystal planes of peaks with the maximum intensityamong peaks of tin dioxide and the half width of the peaks are shown inTable 3.

TABLE 3 Surface temperature of current collector substrate Crystal planeHalf width Comparative example 1 300° C. (200) 2.80° Comparative example2 350° C. (200) 1.31° Comparative example 3 380° C. (200) 1.10° Example2-1 400° C. (200) 1.00° Example 2-2 420° C. (200) 0.91° Example 2-3 450°C. (200) 0.68° Example 2-4 500° C. (200) 0.64°

Further, the x-ray diffraction patterns of tin dioxide coatings in thepositive electrode current collectors of Comparative Example 1, Example2-1, and Example 2-4 are shown in FIG. 5. The encircled peaks in FIG. 5were attributed to titanium.

In the x-ray diffraction pattern of Comparative Example 1, the peakcurves of the respective crystal planes were very gentle slopes. Thehalf width of the peak of the (200) plane was wide. The crystallinitywas supposed to be very low.

On the other hand, in the x-ray diffraction pattern of Example 2-1, thepeak curves of the respective crystal planes were steep. The half widthof the peak of the (200) plane was narrow. The crystallinity wassupposed to be high. In the x-ray diffraction pattern of Example 2-4,the peak curves of the respective crystal planes were steeper. The halfwidth of the peak of the (200) plane was narrower. The crystallinity wassupposed to be very high.

As shown in Table 3, in the case where the heating temperature was 300°C. (Comparative Example 1), 350° C. (Comparative Example 2), or 380° C.(Comparative Example 3), the crystallinity was low and the half widthwas higher than 10. In the case where the heating temperature was 400°C. in Example 2-1, the half width was 1.00°. Further, in the case wherethe heating temperature was 420° C. in Example 2-2, the half width was0.91°. Further, in the case where the heating temperature was as high as450° C. (Example 2-3) and 500° C. (Example 2-4), the crystallinity wassufficiently high and the half width was sufficiently low than 10.

(2.2) Results of Life Performance

For lead-acid batteries produced using the positive electrode currentcollectors of Comparative Examples 1, 2, and 3 and Examples 2-1, 2-2,2-3, and 2-4, the life performance test was carried out. The method forthe life performance was the same as in the first embodiment.

Results of the life performance test are shown in FIG. 6. The abscissaaxis of FIG. 6 shows the half width of XRD peak with the maximumintensity and the ordinate axis shows the life performance. Thedefinition of the life performance is described in the first embodiment.

The life performance of the positive electrode current collectors ofExamples 2-1, 2-2, 2-3, and 2-4 exceeded 400 days. However, the lifeperformance of the positive electrode current collectors of ComparativeExamples 1, 2, and 3 was 200 days or shorter.

According to the above-mentioned results, in the case where the halfwidth of peak with the maximum intensity among peaks of tin dioxidebecame 1° or lower in the x-ray diffraction pattern of the positiveelectrode current collector, the life performance became excellent.

(3) Third Embodiment

In a third embodiment, how the number of selectively oriented crystalplanes affected the life performance of the lead-acid battery wasinvestigated.

(3.1) Production of Positive Electrode Current Collector

The spraying amount of the raw material solution per one time in theproduction process affects the number of the selectively orientedcrystal planes. Further, whether annealing treatment is carried out ornot for titanium to which spraying is carried out also affects thenumber of the selectively oriented crystal planes. Therefore, titaniumwhich was not annealed and titanium which was annealed were used toproduce positive electrode current collectors. The spraying amount ofthe raw material solution per one time was variously changed.Hereinafter, specific explanation will be given.

Using titanium which was not annealed as a current collector substrate,the raw material solution was intermittently sprayed. In the case ofspraying, the spraying amount per one time was changed to be 0.2 cc, 0.4cc, 0.6 cc, and 0.8 cc to form a titanium dioxide coating on the currentcollector substrate. The heating temperature of the current collectorsubstrate was 550° C.

Further, using titanium which was annealed in vacuum atmosphere as acurrent collector substrate, a titanium dioxide coating was formed onthe current collector substrate by adjusting the spraying amount pertime to be 0.2 cc and 0.4 cc. The raw material solution was the same asin Example 1.

(3.2) Results of X-Ray Diffractometry

In the case where the spraying amount was 0.2 cc/time, there were 2selectively oriented crystal planes. In the case where the sprayingamount was 0.4 cc/time, there were 4 selectively oriented crystalplanes. In the case where the spraying amount was 0.6 cc/time, therewere 5 selectively oriented crystal planes.

As described above, as the spraying amount was increased more, thenumber of the selectively oriented crystal planes was increased more. Itis supposed to be because the heating temperature was high and theambient temperature in the periphery of the current collector substratewas so sufficiently increased as to cause the thermal decomposition andalso because, similarly to the case of a dip coating method, due to theincreased thickness of the liquid film of the raw material solutionsprayed to the surface of the current collector substrate, crystals werecontained which were grown using crystal cores in crystal planes invarious directions produced in the liquid film without using the crystalon the surface of the current collector substrate as the undercoatinglayer.

In the case of using the current collector substrate of titanium whichwas annealed in vacuum atmosphere, in the case where the spraying amountper one time was set to be 0.2 cc, there was one selectively orientedcrystal plane and in the case where it was set to be 0.4 cc, there werethree selectively oriented crystal planes.

The above-mentioned results are collectively shown in Table 4.

TABLE 4 Current collector Spraying amount per Number of selectivelysubstrate one time oriented crystal planes Titanium not annealed 0.2 cc2 0.4 cc 4 0.6 cc 5 0.8 cc 6 Titanium annealed in 0.2 cc 1 vacuumatmosphere 0.4 cc 3

(3.3) Results of Life Performance

The life performance test was carried out for 5 kinds of positiveelectrode current collectors produced in the third embodiment. Themethod of the life performance test was the same as in Example 1.

The results of the life performance test are shown in FIG. 7. In FIG. 7,the abscissa axis shows the number of the selectively oriented crystalplanes and the ordinate axis shows the life performance.

According to FIG. 7, in the case where the number of the selectivelyoriented crystal planes was 1 or more and 4 or less, the lifeperformance was excellent. However, in the case where the number of theselectively oriented crystal planes was 5 or more, the life performancewas considerably inferior as compared with that in the case where thenumber was 4 or less. There was significant difference of lifeperformance between the case of 4 and the case of 5.

It is supposed that the life performance was inferior in the case wherethe number of the selectively oriented crystal planes was 5 or morebecause the points where crystals of different crystal planes areadjacent to one another are increased and therefore the chemicalstability is lowered.

The present invention relates to a positive electrode current collectorfor a lead-acid battery having a coating on the surface. A lead-acidbattery equipped with the positive electrode current collector showsextremely excellent life performance. Accordingly, the present inventioncan be applied widely in industrial spheres.

1: A positive electrode current collector for a lead-acid batterycomprising a coating of tin dioxide formed on the surface of a currentcollector substrate of titanium or a titanium alloy, wherein the halfwidth of a peak with the maximum intensity among peaks of tin dioxide inthe x-ray diffraction pattern of said positive electrode currentcollector for a lead-acid battery is 1° or lower. 2: A positiveelectrode current collector for a lead-acid battery comprising a coatingof tin dioxide formed on the surface of a current collector substrate oftitanium or a titanium alloy, wherein crystals of said tin dioxide areselectively oriented in 1 or more and 4 or less of the crystal planes.3: The positive electrode current collector for a lead-acid batteryaccording to claim 2, wherein said crystal planes oriented are a (110)plane, a (101) plane, a (200) plane, a (211) plane, a (220) plane, a(310) plane, a (112) plane, or (301) plane. 4: The positive electrodecurrent collector for a lead-acid battery according to claim 1, whereinsaid coating contain antimony or fluorine. 5: A lead-acid batterycomprising said positive electrode current collector according toclaim
 1. 6: The lead-acid battery comprising said positive electrodecurrent collector according to claim
 4. 7: The positive electrodecurrent collector for a lead-acid battery according to claim 2, whereinsaid coating contain antimony or fluorine. 8: The lead-acid batterycomprising said positive electrode current collector according to claim7. 9: The positive electrode current collector for a lead-acid batteryaccording to claim 3, wherein said coating contain antimony or fluorine.10: The lead-acid battery comprising said positive electrode currentcollector according to claim
 9. 11: A lead-acid battery comprising saidpositive electrode current collector according to claim
 2. 12: Alead-acid battery comprising said positive electrode current collectoraccording to claim 3.